The purpose of this document is to define mental retardation and answer questions related to this topic. According to the American Association on Mental Retardation (AAMR), mental retardation is a disability that occurs before age 18. It is characterized by significant limitations in intellectual functioning and adaptive behaviors as expressed in conceptual, social and practical adaptive skills. It is diagnosed through the use of standardized tests of intelligence and adaptive behavior. The following questions are answered in this document: (1) What assumptions are essential to applying this definition? (2) What is intelligence? (3) What is adaptive behavior? (4) How do cognitive and intellectual disabilities such as mental retardation affect individuals? (5) How can supports help? (6) What is the definition of developmental disabilities (DD)? (7) How does the DD definition compare with the AAMR definition of mental retardation? (8) What does The Arc mean by related developmental disabilities? (9) How many people are affected by mental retardation? and (10) Is it necessary to continue to use the term ?mental retardation??